The present invention relates to a battery charger including a hybrid bridge or a semicontrolled bridge rectifier circuit adapted to rectify the output of an AC generator to charge a battery.
A conventional battery charger of this type includes thyristors having the anodes respectively connected to the input terminals of the rectifier circuit and having the cathodes connected to each other to form the positive output terminal of the rectifier circuit and diodes having the cathodes respectively connected to the input terminals of the rectifier circuit and having the anodes connected to each other to form the negative output terminal of the rectifier circuit. There is provided a coupling device for coupling the gates of the thyristors to the input terminals of the rectifier circuit to provide gate signals, and a disabling device for disabling the coupling device when the battery terminal voltage exceeds the reference value. Disadvantages of the conventional battery charger includes: that the voltage fluctuation is substantial, that the power loss in the thyristors is substantial, that charging current cannot be conducted unless the generator is driven at relatively high speeds, and that there is a difficulty in cooling the thyristors. The reason for these disadvantages will be later described in detail, and it is just mentioned here that these disadvantages are mainly due to the facts that the gate currents flow through a path including the battery, that the cathodes of the thyristors are connected to each other and that the anode of the thyristors are at different potentials from each other.